(Field of the Invention)
The present invention relates to a motor driving circuit apparatus for a motor actuator. More particularly, the invention is concerned with a motor driving circuit apparatus for use in a motor actuator of the type having a control means for inputting a driving control signal for the motor, a sensor adapted to output a signal corresponding to the position of the actuator, and a comparator section adapted to compare the input through the control means and the output from the sensor, the comparator being adapted to produce an output signal in accordance with which the motor is driven and controlled, the motor driving circuit apparatus characterized in that the time duration in which the driving control is conducted is limited by a timer.
(Description of the Prior Art)
FIG. 1 shows a known motor actuator having a motor 1 adapted to rotate a valve 2 through an angle .theta. between two positions A and B. Generally, the motor driving system of a motor actuator of the kind described incorporates a control means (not shown) for inputting a command position information and a sensor (not shown) for outputting the position information concerning the position of the valve 2. The motor driving system has a servo mechanism which is operated in response to the input from the control means and the output from the sensor so as to drive the motor 1 forwardly or reversely in order to rotate the valve 2 to a desired position. The motor 1 is stopped when the output from the sensor has become equal to the input through the control means, i.e., when the valve 2 has reached the command angular position appointed by the input delivered through the control means. In the operation of this motor actuator, however, it is quite likely that the valve is locked during rotation due to some obstruction while the driving current is being continuously supplied to the motor 1. This state is usually referred to as "motor lock". When the motor is continuously supplied with the driving current in the state of motor lock, the motor 1 is burnt out or otherwise damaged.